Question: Which of these numbers is composite? ${17,\ 37,\ 53,\ 77,\ 79}$
Solution: A composite number is a number that has more than two factors (including 1 and itself). 17, 37, 53, and 79 each have only two factors. The factors of 77 are 1, 7, 11, and 77. Thus, 77 is the composite number.